Src Family Kinase Inhibitors Bosutinib and Dasatinib Enhance ATRA-induced Differentiation of NB4 Leukemia Cells

BACKGROUND/AIM: Acute promyelocytic leukemia (APL) has been treated for decades with all-trans-retinoic acid (ATRA) and arsenic trioxide (ATO), which achieve excellent survival but remain limited by induction mortality, ATO-related toxicities, and relapse in some patients. Src family kinases (SFKs) regulate proliferation and survival of myeloid lineage cells, and SFK inhibition has been reported to enhance retinoic acid (RA)-induced differentiation. We investigated whether clinically available SFK inhibitors can augment ATRA-induced differentiation of APL-derived NB4 cells more effectively than the ATRA plus ATO standard regimen. MATERIALS AND METHODS: NB4 cells were treated with PP2, bosutinib, or dasatinib with or without ATRA. Differentiation was assessed by CD11b expression using flow cytometry and by nitroblue tetrazolium reduction. SFK phosphorylation and retinoic acid receptor (RAR) target gene expression were evaluated by immunoblotting. Apoptosis was analyzed to distinguish differentiation from cytotoxic effects. RESULTS: <0.05). Enhanced granulocytic differentiation was confirmed by nitroblue tetrazolium reduction and was not accompanied by increased apoptosis. SFK inhibitors reduced SFK phosphorylation and increased RAR target protein expression in parallel with augmented differentiation. CONCLUSION: Clinically available SFK inhibitors, particularly dasatinib, synergistically enhance ATRA-induced myeloid differentiation of NB4 APL cells and are more effective than the conventional ATRA plus ATO combination in this in vitro model. These findings support further preclinical and clinical evaluation of SFK inhibitor plus ATRA combinations as differentiation-oriented strategies and potential alternatives or complements to ATO-containing regimens in APL.